Non Liouvillian Colliders Presentation on the occasion of Lagarrigue’s prize to Michel della Negra

Carlo Rubbia Senator for life of the Italian Republic

Della Negra_Dec.2015 1

Original colliderʼs patent by Wideröe, 8th Sept 1943

Della Negra_Dec.2015 The initial proposal of colliding beams Slide# : 2 From storage rings to colliders ● Main conceptual progress in the fifties ➩ MURA ➩Frascati (Bruno Touschek) ➩Novosibirsk (Gersh Budker) ● Two great skepticisms: ➩ Luminosity (rates) and ➩Beam-gas background ● The success of e+-e- colliders at Frascati: ADA, ADONE ● The p-p collisions: ISR at CERN. The beginning of a far more “difficult” physics. “Two swiss watches” in collision ! ● The p-pbar collisions: p-bar accumulation and the beam- beam tuneshift problem. Fewer particles, higher tuneshift! ● The pessimism about operability of the p-pbar collider was conjugated with a widespread lack of confidence in hadron collisions (ISR), when compared for instance with e+ -e-.

Della Negra_Dec.2015 Slide# : 3 Initial Cooling Experiment (ICE)

● In 1977, in a record-time of 9 months, the magnets of the g-2 experiment were modified and used to build a proton/ antiproton storage ring: the "Initial Cooling Experiment" (ICE). ● It served for the verification of the cooling methods to be used for the "Antiproton Project". Stochastic cooling was proven the same year, electron cooling followed later. ● Electron cooling was provided by an "e-cooler" located in a straight section of the ring. ● With some modifications, the cooler was later transplanted into LEAR (Low Energy Antiproton Ring) and then, with further modifications, into the AD (), where it cools antiprotons to this day.

Della Negra_Dec.2015 Slide# : 4 Antiproton cooling in 2 sec !

Della Negra_Dec.2015 Slide# : 5 The CERN-AA accumulator

● 2 years after approval, the first antiprotons were accumulated in summer 1980.

Della Negra_Dec.2015 Slide# : 6 (AA) and Antiproton Collector (AC)

Della Negra_Dec.2015 Slide# : 7 UA1-The first of a new breed of detectors for hadron colliders

● The reason of lack of success of ISR –where most of the discoveries were missed – was due to insufficient quality of detectors ● Detection for e+-e- was simple, since the events are already selected in the s-channel ● In the hadronic channel one is in presence of a high -26 2 background, since for instance σinel = 3 x10 cm and -34 2 -9 σW,Z = 10 cm ➡ signal/noise = 3 x10 . ● UA1 experiment has been the first of new “hermetic” and 4π detectors, later followed at LEP and LHC, solving: ➥ The trigger problem ➥ The signature problem

Della Negra_Dec.2015 Slide# : 8 52 authors < 1/100 of LHC !

Della Negra_Dec.2015 Slide# : 9 UA1!

UA2!

Della Negra_Dec.2015 Slide# : 10 Two major innovations ● Look directly at constituents (quarks and gluons) beyond fragmentation, with the help of a sophisticated 4 π calorimetry ➡ Energy flow

● Missing energy to identify escaping neutrino or non interacting particles ➡ “Ermeticity” down to 0.2 °

Della Negra_Dec.2015 Slide# : 11 Hadronic events

Schematic function in each of the elementary solid angle Over all energy balance for ordinary elements constituting the events detectorʼs structure

Della Negra_Dec.2015 Slide# : 12 And fast it was !

Della Negra_Dec.2015 Slide# : 13 The initial discovery of the W signal

Neutrino detection by missing energy balance

Della Negra_Dec.2015 Slide# : 14 Decay angular asymmetry of the Correlation of electron electron in the rest frame of the W and neutrino energies! (Parity violation)!

Della Negra_Dec.2015 Slide# : 15 The initial discovery of the Z signal

Lego plots of Z events!

Della Negra_Dec.2015 Slide# : 16 Somewhere in Sweden…..

Della Negra_Dec.2015 Slide# : 17 W-mass determinations

W→eν channel

Della Negra_Dec.2015 Slide# : 18 Anticipating discoveries with higher order diagrams ? ● After the Zo discovery with p-pbar, its detailed studies of the Zo at LEP in very clean conditions have been an essential phase. ● Higher order QM corrections at LEP have anticipated the discoveries of both the top quark and of them Higgs scalar. mtop Higgs

LEP1 LEP2 MH between 114 and ~200 GeV

Experimental discovery LEP2 = 125 - 127 H M GeV

Experimental discovery 2012 Della Negra_Dec.2015 Slide# : 19 The Fermilab Tevatron

Della Negra_Dec.2015 Slide# : 20 Fermilab Accelerator chain

● Main p injector (120 GeV) ● Target: p-bars with a nickel target ● Antiproton source: triangular shaped ring accumulating p-bar with stochastic cooling at 8.9 GeV/c ● Recycler:permanent magnet ring with electron cooling for additional pbar storage at 8.9 GeV/c ● Tevatron: the p-pbar storage ring at 980 Recycler GeVx2 in c. of m.

Main Inj.

Della Negra_Dec.2015 Slide# : 21 The discovery of the top quark

● The first observation of single top quark production using 3.2 fb−1 of pbar-p collision data with √s = 1.96 TeV collected by the Collider Detector at Fermilab (61 institutions). ● The significance of the observed data is 5.0 s.d. The cross section is 2.3±0.6 pb. ● First evidence for the production of single top quarks at the Fermilab Tevatron pbar-p collider and 0.9 fb−1 dataset (84 institutions) ● The cross section is 4.9 ± 1.4 pb, corresponding to a 3.4 standard W+highest-pT b-tagged jet The expected signal is shown from the deviation significance. measured cross section

Della Negra_Dec.2015 Slide# : 22 Conclusion: Impact of p-pbar on HEP ● Since its initial introduction in HEP in 1982, the p-pbar technology firstly at CERN and later at Fermilab has dominated the highest energy sector over the last 27 years, transforming with the help of pbars the two major existing accelerators into colliders with remarkable luminosities: Linit (ppbar)=2.78 x 1032 cm-2, ISR(pp)=1.4 x 1032 cm-2. ● The cooling technologies have been generalized and the accumulation rate has been greatly increased mostly with the help of Van Der Meer cooling and later also with Budker’s cooling both at CERN and at FermiLab. ● On the other end of the energy spectrum, very low energy pbar (LEAR) have permitted very fundamental discoveries. ● Equally revolutionary have been the associated development of instrumentation with the 4π “hermetic” detectors (UA1), hadron calorimetry (Schopper) and drift chambers (Charpak) which have ensured even with “Swiss watches” a detection + - Dellacapability Negra_Dec.2015 comparable to the one of e e . Slide# : 23 The Higgs, the latest Nobel winning discovery ! ● CMS and Atlas have observed in 2012 with LHC a narrow line of high significance at about 125 GeV mass, compatible with the Standard Model Higgs boson.

➩ATLAS: mH = 125.5 ± 0.2 (stat) ± 0.6 (sys) GeV

➩CMS: mH = 125.8 ± 0.4 (stat) ± 0.4 (sys) GeV ● Their data are consistent with fermionic and bosonic coupling expected from a SM Higgs particle. ● Searches have been performed in several decay modes, however in the presence of very substantial backgrounds. ● Experimental energy resolutions have been so far much wider of any conceivable intrinsic Higgs width. ● Results of both experiments also exclude other SM Higgs bosons up to approximately 600 GeV.

Della Negra_Dec.2015 Slide# : 24 The LHC observation of the Higgs at 125 GeV

Signal and background in the H -> 2 γ channel

CMS ATLAS

Della Negra_Dec.2015 Slide# : 25 The Higgs width according to the Standard Model

● Cross section for the Higgs is shown here, convoluted with a Gaussian beam distribution. ● Signal is not affected only if the rms beam energy width is ≤ a few MeV. ● Like in the case of the Zo,

the Ho width will be crucial in the determination of the nature of the particle and of the associated underlying phenomenology 4.5 MeV width: The very demanding resolution R ≈ 0.003% is required Della Negra_Dec.2015 Slide# : 26 Stability of the Higgs sector ● For the experimental value, the electroweak vacuum is meta- stable, but with a lifetime longer than the age of the Universe. ● The Standard Model may be valid without new physics all the way up to the Planck scale.Thus, there may be only one standard model (SM) Higgs and no need for the “no fail theorem” and no immediate necessity of SUSY at LHC energies.

Della Negra_Dec.2015 Slide# : 27 arXiv:1310.0763v3 [hep-ph] 30 Dec 2013

Ultimate LHC uncertainties are due to systematic effects ● The estimates reflect one of LHC detectors accumulating 300 fb−1 of data, dominated at this level by systematic errors of the ATLAS and CMS collaborations at the best understanding. l ATLAS and CMS arXiv:1207.2516v3 [hep-ph] 1 Apr 2013 have estimated LHC 300fb-1 errors also for 3000 fb−1 from +5% the High-L LHC. l However such estimates can -5% hardly be a σ 1 uncertainty straightforward extrapolation of the current performances. Della Negra_Dec.2015 Unambiguous discoveries require 5 σ Slide# : 28 The future: studying the Higgs signal beyond LHC ● A comprehnsive Higgs study requires √s energies of up to ≈ 1.0 TeV, and adequate luminosities. Two main alternatives are: ● e+e- colliders at L > 1034, with huge dimensions and cost, namely ➩a ≈ 100 km ring (4xLHC), but limited to √s < 250 GeV, thus missing many Higgs-strahlung and Higgs-Higgs boson diagrams ➩a Linear Collider (ILC), eventually to √s ≈ 1 TeV and ≈ 50 km. This is a major new technology which needs to be developed. ● These projects will largely exceed LHC costs and time schedule. ● µ+µ- rings, with a much lower cost and of a much shorter time schedule and which may easily fit within the existing CERN site, but requiring the compression in phase space of muon beams, with two potential main alternatives: ➩the s-channel resonance and L > 1032 at √s = 126 GeV in order to observe its 4 MeV wide Higgs width without backgrounds; ➩A higher energy collider ring, eventually up to 1 TeV and a L > 1034 and luminosity comparable to a e+e- Linear Collider. Della Negra_Dec.2015 Slide# : 29

Requirements for the Higgs with a e+e- ring collider ● The luminosity is pushed to the

beam-strahlung limit. σx/φ ● Collisions are at an angle, but with 2φ fewer bunches than for a B-Factory: a nano-beam scheme σz l Luminosity (several x 1034 cm-2 s-1), costs and power consumption (≈100 MW) are comparable to those of a linear collider ILC. l In order to reach luminosity (factor ≈ 500 x LEP2) and power

consumptions ( factor 5 x LEP2) the main cures are 30 Ø Huge ring (80 km for SuperTristan or for T-LEP) Ø Extremely small vertical emittance, with a beam crossing size the order of 0.01 µ (it has been 3 µ for LEP2)

l The performance is at the border of feasibility (Ecm≈ 250 GeV). l The Higgs width, H-strahlung and double Higgs diagrams cannot be studied by any acceptable e+e- ring collider. Della Negra_Dec.2015 Slide# : 30 The Linear collider option ● The International Linear Collider (ILC) is a high-luminosity linear electron-positron collider based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating technology. ● Its energy √s is 200–500 GeV (extendable to 1 TeV).

LINAC at 25 MeV/m

Two sub micron beams LINAC at 25 MeV/m colliding once head-on ILC, CLIC, NLC, JLC +…

The total footprint for 500 GeV is ∼31 km. To upgrade the machine to Ecms = 1 TeV, the linacs and the beam transport lines would be extended by another ∼ 22 km. Della Negra_Dec.2015 A comprehnsive Higgs study requires √s ≈ 1 TeV, Slide# : 31 Main parameters of ILC ● Collisions between electrons and positrons, with many bunches of 5 nanometres (0.005 µ !) in height, each containing 2 x 1010 particles and colliding 14,000 times per second. ● 16,000 SC accelerating cavities made of pure niobium. ● Temperature: 2 K (-271.2 °C); Accelerating Gradient: 31.5 MV/m ● Length: 31 km for 500 GeV extended to 50 km for 1 TeV plus two damping rings, each with a circumference of 6.7 km (1/4 LHC). ● Nearly 300 laboratories and universities around the world are involved in the ILC: more than 700 people are working on the accelerator design, and another 900 people on detector development. ● The accelerator design work is coordinated by the Global Design Effort, and the physics and detector work by the World Wide Study. ● The estimated cost for the 500 GeV option is ≈ 8 Billion $(2012). Della Negra_Dec.2015 Slide# : 32 Higgs related higher order electroweak processes ● (A) Production cross sections (A) (B) of Higgs boson from e+-e-or µ+- µ- as a function of the energy √s ● (B) Production cross sections from e+-e-or µ+-µ- -> HX as a function of the √s energy 80 km e+e- ring at CERN ➩The Higgs-strahlung diagram (Left), the W-boson fusion process (Middle) and the top-quark association (Right). ➩Double Higgs boson diagrams via off-shell Higgs- strahlung (Left) and W- boson fusion (Right) processes In order to study comprehensively all these processes energies of 0.6-1 TeV are needed Della Negra_Dec.2015 Slide# : 33 The alternative: cooling with non Louvillian Accelerators ● Already at MURA in the fifties it was realised that some beam phase-space compression may be often necessary from the source to the collision point (O’Neill, Piccioni, Symon). ● Liouville theorem: whenever there is an Hamiltonian (i.e. any force derivable from a potential) then the six dimensional phase space is preserved, namely, at best ΔV/dt =0. ● Therefore we need some kind of dissipative non-Liouvillian drag force working against the particle speed and not derived from an Hamiltonian. Several alternatives are possible: ➩Synchrotron radiation: but only for electrons and positrons; ➩Electron cooling: an electron beam bath travelling with a speed equal to the one of the circulating beam (Budker) ➩Stochastic cooling: statistcal fluctuations (Van Der Meer) ➩Ionization cooling: dE/dx losses are added to the beam ● With any of such methods and with accelerating cavities replacing the losses, one can compress the phase-space volume.

Della Negra_Dec.2015 Slide# : 34

From antiprotons to muons ● Phase compression (cooling) is essential whenever secondary particles are produced from initial collisions and later accelerated, to be accumulated in a storage ring. ● A well known case is the one of antiprotons, in which both stochastic and electron cooling have been vastly used. P-pbar colliders have permitted the discoveries of W/Z and the Top. ● Ionization cooling is specific for muons, since they have only electromagnetic interactions with matter ● The muon lifetime may be long enough to offer with the help of ionization cooling a reasonable number of µ+ µ- collisions in a ring in which they interact head-on. ● The idea has been discussed by Budker and Skrinsky in the seventies. A comprehensive analysis has been given f.i. by Neuffer in the early nineties. T. Neuffer Particle Accelerators 1983 Vol. Della Negra_Dec.2015 Slide# : 35 14 pp. 75-90 The development of ionization cooling ● This method, called “dE/dx cooling" closely resembles the synchrotron compression of relativistic electrons — with the multiple energy losses in a thin, low Z absorber substituting the synchrotron radiated light. ● The main feature of this method is that it produces an extremely fast cooling, compared to other traditional methods. This is a necessity for the muon case. ● Transverse betatron oscillations are “cooled” by a target “foil” typically a fraction of g/cm2 thick. An accelerating cavity is continuously replacing the lost momentum. ● Unfortunately for slow muons the specific dE/dx loss is increasing with decreasing momentum. In order to “cool” also longitudinally, chromaticity has to be introduced with a wedge shaped “dE/dx foil”, in order to reverse (increase) the ionisation losses for faster particles.

Della Negra_Dec.2015 Slide# : 36 Muon cooling ring: transverse emittance

● The emittance εΝ evolves whereby dE/dx losses are balanced by multiple scattering (Neuffer and McDonald):

Cooling Scattering2 * * d" " dE $ (13.6) β = beta at cross Xo = Rad. Length # 2 + 3 %0 mµ,βµ = mu values dE/dz = ioniz. Loss dz $ E dz 2$ Emµ X o l The cooling process will continue until an equilibrium transverse emittance has been reached: * 2 ! $ (13.6 MeV /c) 1 "N # 2$µ mµ (X o dE dz)

l The equilibrium emittance εΝ and its invariant εΝ/βγ are shown as a ! function of the muon momentum. l For H2 and β*= 10 cm, εΝ/βγ ≤ 700 mm mr from 80 to 300 MeV/c

Della Negra_Dec.2015 Slide# : 37 ! Muon cooling ring: longitudinal emittance lLongitudinal balance is due to heat producing straggling balancing dE/dx cooling. A dE/dx radial wedge is needed in order to exchange longitudinal and transverse phase-spaces. lBalancing heating and cooling for a Gaussian distribution limit: Intrinsic Energy loss Wedge shaped absorber Straggling 2 2 d "E d("E) 2 , d $ dE o ' dE $ d* ' + / ( )straggling = #2("E) . f A & ) + fA & ) 1 + dz - dE % ds ( ds % dx ( E* 0 dz

Ø dE dz = f A dE ds , where fA is the fraction of the transport length occupied by the absorber, which has an energy absorption coefficient dE ds ! Ø η is the chromatic dispersion at the absorber and δ and d " dx ! are the thickness and radial tilt of the absorber 2 2 d "E m c 2 2 1 Ø the straggling (H2) is given by ( )straggling #( e ) ($ + ) ! = dz 4ln(287)%X o ! Della Negra_Dec.2015 Slide# : 38

! Longitudinal balance (cont.) ● The thickness of the absorber must vary with the transverse position, producing the appropriate energy dependence of energy loss, resulting in a decrease of the energy spread From D. V. Neuffer/NIM A 350 (1994) 27-35

● Energy cooling will also reduce somewhat the transverse cooling, according to the Robinson’s law on sum of damping decrements. dE/dx loss as a function 2g⊥ + gL ≅ 2 of the muon momentum for hydrogen (very near to min for 250 MeV/c) Della Negra_Dec.2015 Slide# : 39 µ+µ- colliders for Higgs factories ? ● Cooled muons may offer two alternative experiments: ➩A Higgs ring in the narrow s-channel resonance at √s = 126 GeV, where most decay channels may be accurately measured. ➩A higher energy collider ring eventually up to 0.6÷1.0 TeV. of luminosity comparable to one of a e+e- linear collier ● These rings can easily fit within the CERN site. ➩For √s = 126 GeV the ring radius is ≈ 50 m (about 1/2 of the CERN PS or BNL AGS) and the resolution ≈ 0.003% ➩For √s = 1 TeV the corresponding ring radius is ≈ 400 m (less than ½ of the CERN SPS) and the resolution ≈ 0.1 % ● Both alternatives must cool two bunches, each with 2 x 1012 µ+ and µ-, starting with 5 MWatt protons at ≥ 5 GeV and 10/50 s-1 . ● After cooling, both µ+ and µ- must be accelerated. ● Packed recirculating LINAC structures to 62.5 and 500 GeV may be studied such as also to fit within the existing CERN site . Della Negra_Dec.2015 Slide# : 40 The full muon cooling process at √s = 126 GeV ● Three successive steps are required in order to bring the cooling process at very low energies, after capture and bunching + rotation. 1. Linear transverse cooling of both signs and small Δp increase. 2. Ring cooling in 6D with B brings the µ+ and µ- to a reasonable size Merging and cooling to single bunches

3. Parametric Resonance !! " 20(" )!mm!rad

Cooling (PIC), where !L " 30(" )!mm!rad ! the elliptical motion in x-x' phase space has become hyperbolic.

Della Negra_Dec.2015 Slide# : 41 !! = 0.04(" )mmrad !L =1.0(" )!mm!rad ( PIC, the Parametric Resonance Cooling of muons ● Combining ionization cooling with parametric resonances is expected to lead to muon with much smaller transv. sizes. ● A linear magnetic transport channel has been designed by Ya.S. Derbenev et al where a half integer resonance is induced such that the normal elliptical motion of particles in x-x' phase space becomes hyperbolic, with particles moving to smaller x and larger x' at the channel focal points. ● Thin absorbers placed at the focal points of the channel then cool the angular divergence by the usual ionization cooling. LEFT ordinary oscillations RIGHT hyperbolic motion x x’ = const induced by perturbations near an (one half integer) resonance of the betatron frequency. Della Negra_Dec.2015 Slide# : 42 V. S. Morozov et al, AIP 1507, 843 (2012); Details of PIC ● Without damping, the beam dynamics is not stable because the beam envelope grows with every period. Energy absorbers at the focal points stabilize the beam through the ionization cooling. l The longitudinal emittance is maintained constant tapering the absorbers and placing them at points of appropriate dispersion, vertical β and two horizontal β.

l . Comparison of cooling factors (ratio of initial to final 6D emittance) with and without the PIC condition vs number of

cells:Della Negra_Dec.2015 more than 10x gain Slide# : 43 Bunch acceleration to 62.5 GeV lIn order to realize a Higgs Factory at the known energy of 126 GeV, an acceleration system is progressively rising the energy of

captured muons to mHo/2 lAdiabatic longitudinal Liouvillian acceleration to pf= 62.5 GeV/c. lBoth µ+ and µ- are accelerated sequentially in the same LINAC with opposite polarity RF buckets ● A recirculating LINAC and 25 MeV/m with f.i. 5 GeV energy/ step + multiple bi-directional passages to 63 GeV (≈ 200 m long) ● A similar layout for the second phase with √s ≈1 TeV will require a recirculating length of 1.6 km, still well within CERN site.

D. Neuffer, 2013 Della Negra_Dec.2015 Slide# : 44 Muons collide in a storage ring of R ≈ 60 m ● Lattice structure at the crossing point, including local chromaticity corrections with βx = βy = β* = 5 cm.

Ankenbrandt et al. (1999)

Della Negra_Dec.2015 Slide# : 45 Muon related backgrounds ● A major problem is caused by muon decays, namely electrons from µ decay inside the detector with ≈ 2x103 e/meter/ns, however collimated within an average angle of 10-3 rad. ● A superb collimation is required with the help of absorbers in front of the detector’s straight sections.

Drozhdin, Mokhov et al.

Della Negra_Dec.2015 Slide# : 46 Eatimated performance of the Ho-factory

● Two asymptotically cooled µ Proton energy 5 GeV bunches of opposite signs collide Proton power 4 MW Event rate 50 c/s in two low-beta interaction Protons/pulse 10^14 ppp points with β*= 5 cm and a free Muons, each sign 6 x10^12 pp length of about 10 m, where the Cooled fraction 0.16 Final momentum 62.5 GeV/c two detectors are located. Final gamma 589.5 ● The bunch transverse rms size Final muon lifetime 1.295 ms is 0.05 mm and the µ-µ tune Colliding, each sign 1 x 10^12 pp Collider circumf. 360 m shift is 0.086. Transverse emittances 0.04 mm rad ● A luminosity of 5 x 1032 cm-2 s-1 Bunch transv, rms 51. µ 12 Long emittance 1 mm rad is achieved with 1 x10 µ/bunch. No of turns 1110 ● The SM Higgs rate is ≈ 44’000 No effective turns 555 ev/year in each detector. Crossing/sec 27760 Luminosity 5 x10^32 cm-2 s-1 ● An arrangement with at least Cross section 1.0 x10^-35 cm2 two detector positions is Ev/y(10^7 s) 44’000 reccomanded ! Della Negra_Dec.2015 Slide# : 47 The s-channel Higgs production colliders ● Advantages Ø Large cross sections σ (μ+μ- → h) = 41 pb in s-channel resonance and µ+µ- → ZH of 0.2 pb at 250 GeV. Ø Small size footprint: it may fit within the CERN site Ø No synchrotron radiation and beamstrahlung problems Ø Precise measurements of line shape and total decay width Γ Ø Exquisite measurements of all channels and tests of SM. ➩The cost of the facility, provided cooling will be successful, is less than 1/10 of one of the LHC. ● Challenges. ➩A low cost demonstration of muon cooling must be done first. Ø Muon 2D and 3D cooling needs to be demonstrated Ø Need ultimately very small c.o.m energy spread (0.003%) Ø Backgrounds from constant muon decay Ø Significant R&D required towards end-to-end design Della Negra_Dec.2015 Slide# : 48 Proving the muon cooling : the Initial Cooling Experiment ● Physics requirements and the studies already undertaken with muon cooling suggest that a next step, prior to but adequate for a specific physics programme could be the practical realization of an appropriate cooling ring demonstrator. ● Indicatively this corresponds to the realization of unconventional tiny ring of 20 to 40 meters circumference in order to achieve the theoretically expected longitudinal and transverse emittances of asymptotically cooled muons. ● The injection of muons from pion decays could be coming from some existing accelerator at a reasonable intensity. ● The goal is to prove experimentally the full 3D cooling. ● The other facilities, namely (1) the pion/muon production, (2) the final, high intensity cooling system (3) the subsequent muon acceleration and (4) the accumulation in a storage ring could be constructed later and only after the success of the initial cooling experiment has been confirmed at a low cost. Della Negra_Dec.2015 Slide# : 49 The RFOFO Ionization Cooling ● The design is based on solenoids tilted in order to ensure also bending. The LiH absorbers are wedge shaped to ensure longitudinal cooling.

Two separate, 180* apart injection and extraction pulsed inflectors

Pulsed inflector Della Negra_Dec.2015 Slide# : 50 Comments ● A conventional muon cooling ring should present no unexpected behaviour and good agreement between calculations and experiment is expected both transversely and longitudinally ● The novel Parametric Resonance Cooling (PIC) involves instead the balance between a strong resonance growth and ionization cooling and it may involve significant and unexpected conditions which are hard to predict. ● Therefore the experimental demonstration of the cooling must be concentrated on such a resonant behaviour. ● On the other hand the success of the novel Parametric Resonance Cooling may be a premise for an optimal luminosity, since the expected Higgs rate is proportional to the inverse of the transverse emittance, ● Up to one order of magnitude transverse decrement may be expected from PIC. Della Negra_Dec.2015 Slide# : 51 Conclusion ● Astro-particle Physics accelerators have reached with LHC a construction time of ¼ century and investment of ≈ 10 billion $. ● A e+e- Linear Collider with ≈ 50 km in length (ILC) and √s ≈ 1 TeV is a likely novel option, but with very long timescale and huge costs. Short term approval and construction are rather unlikely. ● In our view, cooling of muons in view of a µ+µ- ring represents a very attractive alternative which should be carefully tested with the help of the tiny and cheap Initial Cooling Experiment. ● If successful, it should permit to proceed with muon cooling at a level suitable for high energy µ+µ- colliders both for ➩single Higgs production in the s-state and √s ≈ 126 GeV with a single conventional ring of≈ 50 m radius (≈ 1.2% of LHC) and ➩√ s ≈ 1 TeV with a ring of ≈ 400 m radius (≈ 10% of LHC) and luminosity comparable to the one of the 50 km long e+e- ILC. ● Provided muon cooling is demonstrated, both options can be constructed within the existing sites for a cost and timescale that are realistic and financially feasible. Della Negra_Dec.2015 Slide# : 52 Thank you and congratulations to you Michel !

Della Negra_Dec.2015 Slide# : 53